I want to report a problem with the wlan connection that occurs randomly. This is new, only since about a week (maybe after an du). After reboot I can not rely that the wlan connection is going to be built. A new configuration with ceni then shows:

Maybe one of those :
- driver issue
- firewall blocking the dhcp offers
- bad reception, interference : the link from the router to your computer may be weaker than the other way round, for instance if the transmitting antenna from the router is not located in a good spot or if the transmitting power of the router is too low. In that case any interference (gsm, microwave, other wifi...) may degrade the signal to the point where it's unusable. Solutions may be to choose a higher transmission power on the router, put the router and/or antennas in a better position.
I used to have this issue mostly when saturating the bandwidth with p2p, the bandwidth would slow to a crawl and sometimes it would be impossible to renew dchp. Same thing, seemed to occur randomly though there was a general pattern of the time of the day it occurred more frequently (probably due to interference in that case).
Haven't completely figured it out, but I think it might be related to driver issues the computer's wifi, a router issue, or the firewall of the router kicking in due to too many connection attempts.
You may want to read about bufferbloat also. It may be that the buffers of the router are full to the point that the dhcp offers all timeout.
The issues are mostly over since I configured QoS of the router, reduced txquelen of the wifi of both the router and the PC, and added traffic shaping (wondershaper) on the PC.
Wifi chip : Atheros AR928X Wireless
Router : Linksys WRT54GL running on latest DD-WRT firmware

10toe

Post subject:Posted: 25.04.2011, 10:34

Joined: 2011-03-05
Posts: 15
Location: Kiel, Germany
Status: Offline

ShakaZ, thanks a lot for your suggestions! I am writing on the said machine via wlan right now - and I think it was (or maybe still is) a combination of driver and interference issue.

I give a short summary:

I gave it a try for a fresh dist-upgrade, but the firmware-b43-lpphy-installer was not available any more (404 error). Too bad, I had to go for the braodcom-sta driver. Okay, seemed to work again, but still "no dhcpoffers".

Then I tried with other adjustments. Class: "Auto" (instead of allow-hotplug) did it - at least for the moment, and only after I cut the "wire-lan" connection. I don't believe that was the real reason. A few days later (today) there is "no dhcp-offer" - again.

So I tried switching through the channels... well, finally, it works. But I have the dim feeling that this was not the end of the game either. Well, I'll wait a few days before I switch the thread to "solved".

Thanks again ShakaZ for your important suggestions!

Offtopic:

This machine is an lenovo G530. I bought it for my wife for her daily office tasks. It was very inexpensive and sold without OS, so I thought it was perfect for our desire.

But what I saved in Euros I payed back - in "hours"...

To tell the truth, I learned that the broadcom wifi card is a pain in linux. So the easiest way would be to change the mini-PCI-card with an atheros-based card or something else. But lenovo does not allow this: the BIOS has a blockade and refuses a boot with "unauthorised" hardware.

Well, just as a warning, in case anyone tinkers with the idea of buying one of these cheap machines, G550 and so on have the same blockade as far as I know. You have to have ...patience. (ok, to be fair, on the other hand everything else on them is "okay").

DeepDayze

Post subject:Posted: 25.04.2011, 13:58

Joined: 2010-09-11
Posts: 616
Location: USA
Status: Offline

@10toe, there are BIOS's that are patched to disable that "hardware blockade" so that you can use ANY wifi card that fits the slot. My Thinkpad T42 has such a patched BIOS and I am using an Atheros card that's normally not supported. Broadcom cards are still a royal PITA these days

kb0hae

Post subject:Posted: 25.04.2011, 14:16

Joined: 2010-09-12
Posts: 50

Status: Offline

Actually there is an easily installed bios patch for at least some IBM matchines. The problem is that IBM wants you to have to use IBM branded mini-pci cards. Non-IBM branded cards will give an error at boot. The patch changes one bit in bios, which disables the IBM brand checking. The patch is reversed if you reset bios to default settings. I installed the patch on a T41, after which the mini-pci card worked fine.

ShakaZ

Post subject:Posted: 25.04.2011, 14:58

Joined: 2011-02-16
Posts: 67

Status: Offline

@10toe : Yes I should have mentioned the importance of channel wrt interference especially in environments with a lot of wifi devices. The wifi channels that are close to each other have frequencies that are partially overlapping, which causes interference. If you're on the same channel as another wifi device there is time sharing and you're reception is dependent on how aggressive the other device is.
Theoretically the best channel is 1 as it is less weakened by obstacles, but then you have to take into account what channels other wifi devices are using.
For instance, in my neighbourhood, there's a free community wifi network that crosses all over the city. It uses channel 1, probably with high powered antennas, so it's impossible to use that channel. Considering other channels used around my place (5,6,6,6,8,11,12), the next best channel is 3 which I'm using.

10toe

Post subject:Posted: 28.04.2011, 19:51

Joined: 2011-03-05
Posts: 15
Location: Kiel, Germany
Status: Offline

Ok, a few days did past, wlan worked 100%. Problem solved - for now.

Thanks for your suggestions of flashing the BIOS. I will consider this in the future. (Hm, it is legal, isn't it?)